This invention relates to lxN fiber optic switches for selectively connecting a first optical fiber to any one of a plurality of optical fibers at a given wavelength or wavelengths, wherein N is equal to or greater than 2 and is equal to the number of output fibers; however there must be at least two output fibers that are not a continuation of the input fiber.
In certain optical systems it is desirable to selectively connect a signal propagating in a first optical fiber to a number of different receiving stations. Alternatively, it may be desirable to connect the signals propagating in a plurality of optical fibers to a single receiver or detector. Heretofore, most types of alternative interconnection systems were bulky, expensive and unreliable.
U.S. Pat. No. 4,753,501 (S. D. Battle) discloses a fiber optic rotary switching device which incorporates a rotating shutter capable of accepting a single input fiber. The input fiber is operatively connected with the rotatable shutter by a floating ferrule so that the fiber is capable of being rotated to a number of different positions without twisting. Situated adjacent the shutter is a housing having a faceplate which incorporates a plurality of output fibers that are selectively aligned end-to-end with respect to input fiber as the input fiber rotates to a variety of preselected, positions. At the point of interconnection of the input and output fibers, all fibers are parallel to a central axis.
In accordance with the teachings of U.S. Pat. No. 4,896,935 (H. Lee) an optical switching device comprises N fixed optical fibers which are located so that one end of each fiber is optically aligned with a center point. A rotatable optical fiber can be aligned end-to-end with any one of the N fixed fibers.
In the aforementioned switches, wherein the optical fibers are connected end-to-end, a loss is incurred due to axial misalignment, angular misalignment and end separation of the two aligned fibers. Single mode fibers are especially sensitive to these coupling misalignments. Furthermore, the alignment tolerances for low loss connections are very stringent, making such devices expensive and sensitive to environmental changes, vibration, mechanical shock, and other external conditions.
The aforementioned loss problem has been addressed in connection with 2-fiber coupler switches; for example, see U.S. Pat. Nos. 4,763,977; 5,146,519 and European Patent 0,048,855. To make this type of switch, a pair of optical fibers are fused together at a narrowed waist region, each fiber being formed of a core and cladding, and each being tapered toward the waist in such a manner as to insure adiabatic propagation of light in the structure.. An optical signal carried by one fiber first passes through a decreasing taper region and then passes through an increasing taper region of one or the other fibers (or both). The coupler is bent in the region of the waist whereby a coupling ratio can be selected between the incoming fiber portions and the outgoing fiber portions. By bending the coupler in the plane in which the two fibers lie, a signal that is input to one of the fibers can be switched between the two output fibers. However, none of these coupler-type switches is capable of coupling light to two or more output fibers that are distinct from the input fiber.